C12(p,p′)<

Abstract

Cross-section and analyzing-power data are presented for the "C(p, p') "C reaction at bombarding energies of 155 and 200 MeV. Comparisons are made with the systematics of data from other energies. Distorted-wave impulseapproximation calculations for the "pion-like" 1+, T = 1 transition to the 15.11-MeV state are successful for q & 280MeV/c, but are substantially smaller than the data at larger momentum transfers. The implications of the data regarding precritical behavior associated with the pion-condensation threshold are discussed. NUCLEAR REACTIONS C(p, p'), E=155 MeV, measured 0(E, 8); E~200 MeV, measured 0(E, 8), A~(8); 8= 6-50, 4 8= 2-3', E"=11-17MeV. DWIA analysis. Precritical phenomena near pion-condensation threshhold. I. INTRPDUCTIONThe recent suggestion" that precritical phenomena associated with the pion-condensation threshhold might be observable in (p, p') reactions has focused attention on the inelastic excitation of the 1', 2'=1 state at 15.11 MeV in "C. This transition is said to be "pion-like" in that the transfer of a virtual pseudoscalar pion requires both spin transfer and isospin transfer (AS= c T =1). If nuclei are sufficiently close to the critical point for pion condensation, the polarization of the medium by the pion field will produce special collective effects. These should appear as enhancements of (p, p') differential cross sections for isovector unnatural-parity transitions in the range of momentum transfer q near 300-450Existing data for the 15.11-MeV transition at F& --155 MeV indeed show a minimum near q =250 MeV/c followed by a prominent second maximum. 4 Microscopic effective-interaction calculations were unable to describe this shape. However, these features are absent in recent data at E =122 MeV (Ref. 5), where the large-q region of the angular distribution is characterized by a shoulder. Microscopic calculations ' were quite successful in reproducing the absolute cross sections for q & 300 MeV/c; above this point they fell signif icantly below the data.Arguments have also been advanced, based on the large-q behavior of the (e, e') transverse form factor for the same transition, that ' C might actually be close to the pion-condensation threshhold. ' ' Analysis of elastic electron scattering data from ' C seems to support this interpretation. ' It has been noted, however, ' that the (p, p') reaction may be a more sensitive probe of pion phenomena than (e, e') reactions. The reasons are related to the longitudinal (o q) nature of the dominant one-pion-exchange process as opposed to the transverse (oxq) nature of virtual photon transfer, although these distinctions are blurred by surface effects for light nuclei. ' ' In order to obtain new and detailed data on this issue, cross sections for the "C(p, p')"C reaction to the 15.11-MeV and nearby states have been remeasured at 155 MeV with particular attention given to the region q & 200 MeV/c. These will be discussed and compared with additional data, including analyzing-power data, at 120 MeV (Refs. 5, 10) and 200 MeV. '~T he tra...

Simultaneous measurements of (p→, p→′) and (Wells1, Wissink2, Bacher3 et al. 1995Phys. Rev. C

“…This behavior has been verified experimen-tally [8] for the 15.11 MeV state in ' C. To obtain appreciable yields and thereby make statistically meaningful measurements in this work, it was therefore necessary to detect the inelastically scattered protons at small laboratory angles. Moreover, because the photon detectors were positioned very close to the target (to maximize the coincident solid angle), it was essential that the unscattered beam be deposited in a well-shielded beam dump far downstream from the target; this would minimize the background seen by the photon detectors, thus allowing for cleaner identification of the true coincident y rays.…”

“…Inspection of Eqs. (8) and (9) shows that certain (p, p' y) observables can access the relative phases between these two sets of terms, whereas singles (p, p') measurements cannot. Further, the form of the photon polarization tensor t;, (k) implies that these terms can only be accessed if the coincident y rays are detected at some angle that lies out of the scattering plane, yet is not normal to it.…”

“…(8) and (9)] dictates that the maximal sensitivity to these observables is achieved if the photons are detected at an angle of 45' with respect to the n direction, i.e. , in a cone 45 out of the scattering plane.…”

“…Early measurements of do/dA and A for this state [8,9], taken at 200 MeV over a broad range of momentum transfer q, provided some of the first detailed comparisons between inelastic scattering data and predictions from then state-of-the-art distorted wave impulse approximation (DWIA) calculations at intermediate energies. These calculations, which had described data measured for this same transition at lower energies reasonably well [8], were found to disagree significantl with the data taken at this higher energy and at larger momentum transfers. It was argued at the time [9] that the deterioration of the agreement between these calculations and the new 200 MeV data might be due primarily to changes in the effective NN interaction encountered at higher energies.…”

Polarization transfer measurements forC12(p→,nDozono1, Wakasa2, Ihara3 et al. 2009Phys. Rev. C5000View full textAdd to dashboardCite

“…scattering at incident energies of about 120 to 800 MeV [11,12,13,14], and the experimental extraction of R L /R T using complete sets of polarization transfer observables in ( p, p ′ )…”